Evaluation of Hydraulic Fracturing in Coal Seam using Ground Microseismic Monitoring and Source Location

Accurate evaluation of the impact range of hydraulic fracturing (HF) in coal seams is the key to optimizing HF design schemes. In this study, multistage HF processes in Well No. 1 of the Xinji No. 2 coal mine were monitored and analyzed using ground microseismic (MS) monitoring technology. An improved particle swarm optimization algorithm and waveform similarity superposition method were used to locate HF-induced MS events with different signal-to-noise ratios. The results showed that the seismic source location points were distributed horizontally within a 120 m range on both sides of the fracturing well, and vertically distributed from − 615 to − 675 m. The MS events envelope method was used to calculate the stimulated reservoir volume (SRV) of nine fracturing sections, totaling approximately 1,977,000 m³, with the largest SRV in Sections Nos. 2 and 6. Through continuous fracture network (CFN) modeling, the overall fracture extension of the HF was revealed to be rectangular and evenly distributed on both sides of the fracturing well. The main direction of the fracture extended outward along the vertical direction, in line with the direction of the injection hole. By calculating the CFN branch index (BI) and CFN length, the results showed that the fracture networks of Sections Nos. 1, 4, and 6 were more complex, and the CFN lengths of Sections Nos. 1, 2, 6, and 9 were longer. Combining the fracture network size, MS event parameters, and SRV, we determined that Sections Nos. 2 and 6 have longer fracture networks, larger HF ranges, and the best HF effect. This study is important for the evaluation of the effective range of HF in coal seams and for the design and parameter optimization of HF schemes.